By passing landmark legislation to create an online health-insurance exchange marketplace, California became the first state in the country to actively embrace the federal Affordable Care Act.

But now, with the legality of one of the plan’s key provisions appearing destined for the Supreme Court, health policy experts here are beginning to wonder whether the very problem that doomed a similar try at insurance overhaul in California – a heavily lopsided insurance pool of high-risk, high-cost patients – could undermine the federal reform plan.